1. Field of the Invention:
The present invention relates to a method of packaging a semiconductor device in which a semiconductor device is attached to a mounting body, such as a substrate or a film carrier, and is connected thereto.
2. Description of the Related Art:
Electronic devices in general employ large numbers of semiconductor devices such as ICs. In these electronic devices, the semiconductor devices are packaged on a substrate by soldering, as disclosed in the specification of Japanese Patent Laid-Open No. 45996/1982. To solder the semiconductor devices to the substrate, a soldering material is supplied between a semiconductor device and the substrate by printing with a solder paste or by disposing solder balls therebetween, the substrate then being heated by placing it on a hot plate.
In this packaging method, since the substrate is heated from below to a temperature corresponding to the melting point of the solder (about 230 .degree. C. in the case of a solder which contains Sn and Pb at the ratio of 60:40) or above, the devices and/or resin coating that are attached to the substrate must be heat-resistant. Further, heating of the substrate may cause it to warp. Also, the electrodes on which soldering is done must be made of a conductive material to which solder can be attached, thereby increasing the production cost and lowering the reliability of the devices.
FIG. 8 shows a method of packaging a semiconductor device on a film carrier which is disclosed in the specification of Japanese Patent Laid-Open No. 135265/1977. A semiconductor device 1 employed in this method has Au plated electrodes 2. A base film 4 which serves as a body of a film carrier 3 and which is made of a polyimide resin is provided with an opening 5. A lead pattern 6 is formed on the base film 4 by a photoetching process. The leads are made of, for example, Cu, and the surfaces of the forward ends thereof which hang over the opening 5 are Sn plated to a thickness of 0.5 m.
To package the semiconductor device on the film carrier, after the semiconductor device 1 is placed on a jig (not shown) with its electrodes turned face up, the film carrier 3 is positioned with respect to the semiconductor device 1 in such a manner that the semiconductor device 1 is located within the opening 5 and that the leads 6 are located above the electrodes 2 with a gap formed therebetween being about 100 m. Next, a heating jig 7 is lowered from above the film carrier 3 to press the Sn plated forward ends of the leads 6 downward and heat them at the same time. The leads 6 are therefore brought into contact with the electrodes 2 while the leads 6 and the electrodes 2 are being heated, so that the Sn coated on the leads 6 melts and is diffused into the Au layer plated on the surfaces of the electrodes 2. As a result, an Au-Sn alloy is formed, and electrical connections between the leads 6 and the electrodes 2 are provided. The heating jig 7 is then raised, whereupon the packaging of the semiconductor device 1 is completed.
As the semiconductor device and the substrate are heated in the previously-mentioned packaging method, the contacted portions of the leads 6 and the electrodes 2 must be heated to a temperature of 500.degree. to 600 .degree. C. by the heating jig 7 in order to form an Au-Sn alloy. This may lead to cracking or degradation of the characteristics of the semiconductor device 1. Further, adjacent pads may be short-circuited by melted Sn plated on the surfaces of the leads 6.
Furthermore, when the semiconductor device is connected to the film carrier, it must be coated or molded with an epoxy, silicon, or polyimide resin by a separate and subsequent process to protect their connected portions. Therefore, the film carrier must be collected after the semiconductor device has been connected thereto, during which process the connected portions may be bent and peeled off. This decreases the production yield.